1. Field of the Invention
The embodiments of the present invention relate generally to a calibration tool and a method for determining the position of an object.
2. Background of the Invention
The use of robots in automated processing systems has become increasingly popular. Robots can often perform repeated tasks with the precision and efficiency generally not achievable through the use of human labor. Moreover, robots can be used in locations where the proximity to moving components or hazardous materials makes the use of human labor in such locations undesirable.
Typically, when power is first supplied to a robot that performs complex or precision movements, the robot must establish one or more reference points or coordinates in each axis through which the robot travels. The establishment of these reference coordinates is commonly called homing. For example, a robot may be homed by jogging the robot, either manually or using an automated sequence, to a reference point. Arrival of the robot at the reference point may be confirmed by manually observing the robots end effector""s position, or by having the effectuator (or other component of the robot) trigger a sensor, such as a limit switch. This sequence is typically repeated until all the reference coordinates for each axis of the robot""s motion has been established (i.e., entered into the robot""s or robot controller""s memory).
Once the reference coordinates have been established, the robot can determine the precise location of the effectuator by referencing the position of the effectuator against the reference coordinates. For example, a stepper motor that provides motion to one axis of the robot may be coupled to an encoder that counts the number of shaft revolutions of the motor. Each shaft revolution is equated to a distance moved by the effectuator. As the controller keeps track of the distance moved as indicated by the controller against the reference coordinated, the precise location of the effectuator may be maintained by the controller. Thus, if the effectuator is to be moved a certain distance from its current position, the controller can signal the motor to rotate a prescribed number of revolutions that can be confirmed by the encoder as part of an open or closed loop system.
FIG. 1 depicts a simplified schematic of a front end 100 of a semiconductor processing system that provides an illustrative example of a robot that requires precise movements to prevent damage to a workpiece. The front end 100 generally includes one or more semiconductor storage cassettes 102 that facilitate the storage of a plurality of substrates, such as semiconductor wafers 112. Typically, the wafer storage cassette 102 includes a housing 104 having at least one open end 116 through which wafers 112 may be transferred into and out of the storage cassette 102. Inside the storage cassette 102 are a plurality of rails 114 are spaced to create a plurality of slots 106. Each slot 106 receives a respective wafer 112.
Typically, a wafer handling mechanism, for example a wafer transfer robot 122, is used to transfer the semiconductor wafers 112 from the wafer storage cassette 102 to the other components of the wafer processing system. Typically, the transfer robot 122 comprises a transfer arm 124 having an end effector or gripper 126 disposed at the end of the transfer arm 124. The gripper 126 may be a wand or an edge clamp that secures the wafer 112 to the robot 122 during the transfer of the wafer. Generally, the gripper 126 of the wafer transfer robot 122 is inserted into the wafer storage cassette 102 to retrieve one of the wafers 112 disposed therein. In order to insure accurate positioning in the gripper 126 (and wafers 112) within the cassette 102, the location of the gripper 126 relative to the cassette 102 is recorded in the robot""s memory when the gripper 126 is in a predetermined position within the cassette 102. An example of such a position is a position that aligns with the center of the wafer 112 when the wafer is properly positioned within the cassette 102.
If the position is recorded incorrectly, the robot 122 may be misaligned with a wafer when transferred to other components of the system or deposit a wafer in a misaligned position relative to the wafer storage cassette 102 as depicted in FIG. 1 by wafer 118. The misaligned wafer 118 may become damaged or damage other wafers. For example, a wafer 120 disposed on the gripper 126 of the transfer robot 122 may come in contact with the misaligned wafer 118 during movement of the wafer 120 that is secured to the robot 122. If the wafers 118, 120 contact one another, one or both of the wafers may become damaged. Moreover, one or both of the wafers 118, 120 may become dislodged. A dislodged or fallen wafer typically requires an operator to shut down the system and remove the wafer before further processing can occur.
Typically, homing of the robot""s gripper in a wafer storage cassette is done manually. An operator must observe the location of the gripper within the cassette to visually estimate the correct position of the gripper. In order to access the cassette when performing this task, the operator is in a position exposed to the range of motion of the robot. Thus, to prevent possible injury to the operator, the processing system is normally shut down so that robot does not inadvertently make contact with the operator, possibly damaging product, tooling or the operator. During periods where the system is shut down, no wafers are processed and valuable production time is lost.
Therefore, a need exists for an improved calibration and method for determining the position of an object.
One aspect of the present invention generally provides an apparatus for determining a position of an object. In one embodiment, an apparatus for determining a position of an object includes a locating plate, a window and a camera. The camera is positioned to view a target through the window disposed in the locating plate. The object on which the target is disposed may be viewed by the camera enabling the relative position between the locating plate and the object to be determined. In another embodiment, the image produced by the camera is viewed on a display remotely located from the apparatus.
In another aspect of the invention, a system for determining a position of an object is provided. In one embodiment, the system includes a target disposed on the object and a portable tool. The tool includes a locating plate coupled to a housing. A window is disposed in the locating plate or the housing and has an indicia disposed thereon. A camera is disposed between the housing and the locating plate. The camera positioned to view the target through the window.
In another aspect of the invention, a method for determining a position is provided. In one embodiment, the method includes the steps of locating a calibration tool in a predefined position, viewing an object thought a window disposed in the calibration tool, and determining the relative position between an indicia disposed on the window and the object.